Broad band-pass circuit arrangement



Oct. 7, 1952 J JASPERS 2,613,268

BROAD BAND-PASS CIRCUIT ARRANGEMENT I Filed May 28, 1948 MAGNETIC FERRITE CORE 4 AMPLIFIER AMPLIFIER MAGNETIC FERRITE CORE R. E K) INPUT FIGQI INVENTOR ALPHONSUS MARIA JACOB%?ERS AGENT Patented Oct. 7, 1952 STATES PATENT 1 I .2,s13,2es,- W I BROAD BAND-PASS'ICIRCUIT ARRANGEMENT r..:ApplicationMay:28, 1948, Serial No. 29,896 ImtheNetherlands June 21, 1947 2?- Claim (01, 11:18:44.

.5. 'Ihis;invention-relates to ,circuitearrangements forgthe! transmission. of. electrical oscillations, more particularlyl,oscillations of every high frequency iallowing thepassage. of a broadband. of frequencies Circuit-arrangements of. this. kind areused, for example, in television. technique, in transmittingand treceiving devices in .which use is, made of frequency modulatiomin carrier-wave telephony utilising a number .of' transmission channels, and .therlike. tion is .to..provide a circuit-arrangement in which an advantageous. transmission .of a frequency 'bandofanyarbitrary width..may;be ensured in an extremely .simple manner. gmgthe; circuit arrangement according to the invention use .is made .off, a selective circuit .ineluding an "inductance coil comprising a core of ferromagnetic material. Coils of this kind are knownwassuch, .The core of the'ferromagnetic material, whichin (this case generally constitutes a closedcircuit, serves to increasetheinductance with'the, same dimensions of the coil as such. Highly "advantageous.results .in this respect have been obtained with cores substantially consisting of. ferromagnetic metal compoundsand' more particul'a-rly"oiiidesexhibiting substantially no electricalconductivity', which substances when made of a "determinedcomposition exhibit-high permeability with comparatively low'losses even-at higher-frequencies. I I ispossibleyby utilising coils comprising cores of such-materialgto obtainoscillatory circuits havingahigl'rselectivity for high frequency. Howeverpuponincreasing frequency, the losses-of the coil? increase rand its permeability decreases, so

thattheusebf such a-coil above a determined frequency; "which" is dependent-upon the nature of the ferromagnetic material, has been considered'toib'e lessii'efficien The invention is based on recognition of the fact that advantage maybetakenof the increase .inzlosses, and the decrease in permeability in determined ranges of frequencies,- if .it is.-essentia1 to obtain acircuit-arrangement whichallows the passage of "a broadband of frequencies. Hitherto for this :purpose it was frequently ensured that :theiselectiye circuitslexhibitediincreased damping :by: iproyidingwresistances .in parallel with the resonantzi circuitslor by combinin'g a numberof circuits by meansof determined-relative couplings to form a band-pass filter. Withamplifier's it is also known totune the resonant circuits serving as coupling elementsbetweenthe=various successive amplifying stages to slightly different frequencies.

.'I?he object of the inven-r In connectiontherewith it The-presentinvention co'nsists, inth-at' .in a circuit-arrangement forgthe transmission-of elec-' trical; oscillations allowing the passage of a broad bandxof frequencies, which comprises at least one selective circuit including an inductance coil which comprises a.-core of ferromagnetic material exhibiting substantially. no electrical .conductivity, the properties'ofhthe-said materialiare chosen to be such in regard to the. frequencies to be transmitted; that the-permeability exhibits a material decrease with increasing frequency withrespectto the frequencieslof the region to be passed.

, (In thiS-0aSe the-GO11 is used vin arange. of frequencies in which theeifectivemvalue of. the permeability is much :smallerthan. the maximum yalue considered-as the optimum one in former uses the yaluenowbeing, for examplafrom onethird to one-tenth .of the last-mentioned value.

An apparent fall in the lpermeability lof the material of. the .a core with increasing frequency also occurs ins-coils comprising? llaminated or finelyedivided iron as a resultiof the .so-called skin effect. vSuch an. effect is ,u'ndesirablefor the subject .of the present .patent application since itfldoesunotileadto the desiredresult. Conselquently the skin effect istrequired to play an unimportantpart only.

j Ithas been foundthat more particularly .with thesaidcoils comprising coreslof mater'ialscontaining ferromagnetic compounds, a suitable compositionof such materials permits of obtainingin the frequency range to be. transmitted, adecreas'e impermeability with increasing frequency such that! the circuitearrangement ex:- hibits an .iadvantageous action as a bandepass filter. a L Theinventionwwillnow.beexplainedinconnection with the accompanying drawingimwhich;

Fig. 1 showsasingle parallel-,resonant circuit .band pass-fi lter; q

, 2 shoWsacoupled parallelresonantcircuit band-passfiltergand: ,Fig. 3 shows-anaerial circuit-employing} band-:pass filter: according to the invention.

That a icircuiticomprising aicore of the-said ferromagneticmaterialexhibitsthedesired-property Jis accounted for by the I fact-that linwthe region in which the permeability decreases upon increasing-frequency, the inductanceqdecreases "to .the..-sam,,e sextant. fMore particularly if usei-"is rna'deiofia paralle'l-:re sonant circuit, such aI-cir- .cuit- -accomm;odatcs itself as? it weretto theiim' pressed frequency and the impedance of the circuit varies with frequency less rapidly than in the case of a circuit comprising a coil without ferromagnetic core and with otherwise the same damping. Such a circuit arrangement is shown in Fig. 1 of the drawing in which a band-pass filter designed to havean impedance which varies with frequency in such manner that as the frequency increases the impedance of the filter increases through to a less rapid extent than if the coil had no core. In this figure, the filter consists solely of a coil I provided with a core 2 of mixed crystal ferrite and a capacitor 3 in parallel therewith.

The relationship between permeability .and frequency in a determined region may be approximately represented by the formula perm. Crfin which C is a. constant and m a quantity which is dependent on the kind of the constitutivematerial of the core. According to the invention, the kind of the material with respect to the frequencies to be transmitted is preferably chosen to be such that the quantity m is comprised between 0.8 and 2 in the region to be transmitted.

It may readily be shown thatjif m=2, the ideal position would be obtained, that is to'say that, when the coil forms partof an oscillatory circuit, the circuit is in resonance for any frequency of the range under consideration. Consequently, the aim will be to approach this position. I 'It has been found that the materials which are known under the name Ferroxcube and which contain ferrite as the principal constituent exhibitlhighly advantageous properties for the purpose in view. This material has a general formula- MO.F2O3, in which M designates a bivalent metal, e. g. Mn, Cu, Ni'or Mg. I It is essential that the material consists of homogeneous cubic crystals and in general will consist of mixed crystals of two or more ferrites.

With respect to circuit-arrangements comprising parallel resonant circuits which pass a band of frequencies widened by means of a parallel resistance, the subject of the invention affords the advantage of obtaining a much more advantageous value of the product of the bandwith and the maximum impedance of the circuit if, for example, the term bandwith is understood to mean the difference between two frequencies at which the impedance drops below a determined portion of the maximum impedance.

' Variation in the composition of the material permits of varying the frequency range in which the relationship between permeability (or losses) and frequency occurs which is optimum for the invention so that band-pass filter action of the circuit-arrangement for different rangesof frequencies may be obtained by suitable choice of the material.

The present invention is applicable to amplifiers comprising parallel resonant circuits of the kind which are required to pass a frequency band of determined width, but it is also applicable to amplifiers for use at video-frequency voltages, in which oscillations of any frequency below a determined limiting frequency are required to be amplified. Furthermore it is applicable to bandpass filters comprising coupled circuits and bandpass amplifiers in which the coupling elements between the various successive stages are constituted by oscillatory circuits which are relatively detuned. Such a circuit is shown in Fig. 2- which comprises two parallel resonant circuits each comprising a coil 4 and 5 respectively coupled together by a core consisting of a, mixed crystal ferrite 6 and 1 respectively and shunted by a capacitor 8 and 9 respectively.

It has been found that particularly advantageous results may be obtained in the range of frequencies comprised between 10 and megacycles/sec.

In thisconnection it may be mentioned that in radio-receivers comprising frame aerials it is known as such to provide the receiving frame with ferromagnetic material in order to ensure better concentration of the magnetic lines of force passing through the frame. The present invention is distinguished from this known devicenot onlyin that there is worked in a range of frequencies chosen in a particular manner with respect to the range of frequencies to be received but also in that the dimensions of the aerial of ferromagnetic material are great with respect'to those of the coil. The latter may be concentrated on a comparatively smalllength of the rod-shaped core. The aerial is preferably positioned in the direction of the magnetic lines of force and may be active as a magnetic dipole bringing about strong concentration of the magnetic lines of force. For similar reasons as the parallel resonance coil with magnetic core as already described, such an aerial will be suitiable, for uniform reception of frequencieslocated within a broad region. An aerial coupling cir-; cuit accordingto the invention is illustrated in Fig. 3 which comprises a primary winding loin the antenna circuit coupled to a secondary winding H by means of a core consisting of a mixed crystal ferrite l2, the secondary being tunedby a condenser l3.

What I claim is:

1. A broad band-pass circuit arrangement, particularly for passing high-frequency electrical oscillations, consisting solely of an inductance coil having a core of ferromagnetic material and a capacitor in parallel with the coil, said core material consisting essentially of a mixed. crystal ferrite, saidcore material having a magnetic permeability ,c='C'fwherein C is a. constant, ,f is a frequency of oscillation, and m is a number lying between 0.8 and 2. 1 y

2. Abroad band-pass circuit arrangement, particularly forpassing high-frequency electrical oscillations, consisting solely of an inductance coil having a core of ferromagnetic material and a capacitor in parallel therewith, said core material consisting essentially of a mixedcrystal ferrite having a magnetic permeability which materially decreases with increasing frequency in .the pass band.

ALPHONSUS MARIA JACOBUS JASPERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS I OTHER REFERENCES Publication: Philips Technical Review, v01. 8, No. 12, pages353-360, Dec. 1946. H I 

